Analog-to-digital converters generally are devices for converting an analog input signal to a digital output signal. Several types of analog-to-digital converters exist, one of these being so-called tracking analog-to-digital converters (ADCs).
In such tracking ADCs, a digital output signal of the ADC is compared (for example by using a digital-to-analog converter) with an analog input signal, and depending on this comparison the digital output signal is modified. With such a tracking ADC, the digital output signal follows or “tracks” changes of the analog input signal, hence the name.
In some applications, more than one analog signal has to be converted to a digital signal. Providing an corresponding plurality of separate ADCs, for example tracking ADCs, consumes a corresponding amount of chip area. On the other hand, simply multiplexing input signals into a tracking ADC and demultiplexing the corresponding output signals may lead to the problem that, in case of significantly different input signals, the amount of time assigned to each input signal for processing is not sufficient to fully track the signal, leading to incorrect digital output signals.
Furthermore, in some applications tracking ADCs are implemented together with a comparator, for example a comparator arrangement to compare a signal with a constant amplitude level, for example a level of zero to detect a zero crossing, e.g. for the purpose of offset compensation. Also in this case, considerable chip area may be needed, and furthermore inherent offsets of the comparator or the tracking ADC may not always be compensatable in such arrangements.